Thermal diazotype method and developer sheet for use therein



Aug. 31, 1965 P. MULLER 3,203,797

THERMAL DIAZOTYPE METHOD AND DEVELOPER SHEET FOR USE THEREIN Filed oct. 16, 1962 United States Patent 3,203,797 THERMAL DIAZOTYPE IVIETHOD AND DEVEL- GPER SHEET FOR USE THEREIN Peter Muller, Port Washington, N. assgnor to Andrews Paper & lChemical `Co., Inc., Long Island, NX., a corporation of New York 'Filed Oct. '16, 1962, Ser. N 230,850 2 Claims. (Cl. 96-49) This invention relates to an improved thermal diazotype printing process and to an improved developer sheet for 4use in such process.

The diazotype reproduction process is based on the sensitivity of the diazo compounds to the short wave length portion of the visible spectrum and to ultraviolet light and also on the capacity of diazo compounds to react with certain compounds generally called couplers to form azo dyes under controlled pH conditions.

Diazotype light sensitive materials are available 'in two general forms:

(1) The two component or dry system in which the backing sheet has a sensitized coating or coatings containing the light sensitive diazo compound, a dye forming coupler and secondary substances such as the acidic stabilizers, salts and glycols which control shelf life, contrast and rate of development. After this type of diazo reproduction sheet has been exposed to actinic radiation behind the master which is to be reproduced, it is eX- posed to moist vapors of ammonia whichinduce after neutralization of the acid components the development of the azo dye in the areas which have not been exposed to light.

(2) The single component or semi-moist system in which the backing sheet has a sensitized coating containing light sensitive diazo compounds and secondary substances such as acidic stabilizers and salts which control the shelf life, contrast and rate of development. After exposure to light behind the master, this type of diazo reproduction sheet is moistened with an aqueous solution containing a dye forming coupler and other compounds which neutralize the acid stabilizers of the diazotype light sensitive layer and thus induce the development of an azo dye in the areas which have not been exposed to light.

Both of these systems have certain recognized difculties and disadvantages. Thus, in the first or two component system, diiculty is encountered with the arnmonia vapors which must be exhausted so as not to annoy and inconvenience the persons present in the printing room. This problem is particularly aggravated in the case of air-conditioned buildings where the ammonia is drawn into the recirculated air. The second or single component system involves the inconvenience of handling and disposing of developing liquids which are particularly troublesome and annoying in business oiiices.

Attempts have been made to overcome these difculties and disadvantages by completely dry development methods, such as the thermal development methods. The thermal development methods heretofore attempted fall into three general classifications:

(l) Single sheet processes which contain in the sheet a light sensitive diazo compound at least one coupler and a stabilizing substance which prevent azo dye formation under ordinary temperatures and conditions, but which permit dye formation under the elevated temperatures encountered in the thermal development equipment. In methods of this type the diazo material generally has insuflicient shelf life, or if they are adequately stabilized, require excessively high temperatures and prolonged exposures thereto with detrimental eifect on the dye. and occasional charring of the paper backing. In addition,

such methods fail to provide the desired density of color.

ice

Furthermore, diiculty is encountered in providing the moisure required for development. v

y (2) Double sheet process using one light sensitive sheet containing the diazo compound and a second sheet containing a dye forming coupler and at least another substance of an alkaline character. The sheets are brought into close contact with each other under elevated temperature controlled conditions to cause `transfer of the dye forming coupler to the light sensitive sheet. The

'double sheet process has not been generallyY successful because of the slow mobility and low volatility of adequate dye forming couplers under conditions which are not detrimental to the dye formed therefrom or the paper material. p

(3) Developer sheet process using one light sensitive sheet containing the diazo compound, a dye forming coupler and a stabilizer and a developer sheet which contains the developing agents and transfers them to the light sensitive sheet under proper thermal conditions. The developer sheet processes heretofore available have been of loweiciency. Frequently very high developing temperatures were needed and the water was driven oi before the ammonia was generated and was able to enter the ,light sensitive layer to create the proper pH conditions.

In other instances using lower developing temperatures, the ammonia was released prematurely at room temperature resulting in a short shelf life and also causing the same inconvenient smell associated with the two component ammonia system.

The present invention pertains to an improved thermal diazo process using a developer sheet and also to an improved developer sheet for use in such process.

It is a particular object of the prevent invention to overcome the diiliculties and disadvantages heretofore encountered and to provide an improved thermal diazo process and developer sheet for use therein in which high rate of synchronized development and printing is maintained; in which the development takes place at moderate temperatures in a reasonable period of time so that no damage is caused to the dyes or-backing sheets; and which producesv prints of very satisfactory dye density and Vin tensity. l

My invention presents the further advantages that it may utilize the standard diazo reproduction sheets used in the two component ammonia system, in which the developer sheet is dry, in which it is not light sensitive, has

an indefinite shelf life, which does not generate adverse odors when subjected to heat, and which may be used one or more times for developing aV sensitizeddiazo re' production sheet.

My invention contemplates the provision of an improved developer sheet inthe form of a backing sheet having applied thereto coating material which includes an organic amine with low vapor pressure at ordinary room temperature which volatilizes at elevated temperatures between and 180 C. A reservoir or source of water is also preferably provided, and this may take the form of salt crystals having water of crystallization combined therewith. Thus, after the diazo reproduction sheet has been exposed to light beneath the master and the developer sheet superimposed thereon and the superimposed sheets exposed to a temperature between 100 and 180 C., the 4organic amine volatilizes and the water is released mixing with the sensitized layer of the reproduction sheet and raising the pH level to permit the coupler to combine with the diazo compound to form an azo dye.

In the accompanying drawing:

FIG. l is a perspective view of a developer sheet embodying my invention;

FIG. 2 is a diagrammatic view showing a master super- 3 imposed upon a diazo reproduction sheet and exposed to light; and

FIG. 3 is a diagrammatic view showing the exposed diazo reproduction sheet superimposed on the developer sheet and being subjected to heat so as to develop the image.`

My irnproved developer sheet is shown in FIG. 1.l

It comprises a suitable backingsheet, as .'shovvn,n made of suitable material suchas paper, iher board, plastic or metal, whichl is inert te the coating materials applied thoroto ood also to tho materiels io the diazo sensitized loyer of tho 'reproduction Shoot The basking- Shoot Should either bo Sooiootly absorbent to. 12o, Partially Progootoo with tho. ooetne motor-tels. if it, is not absorbent, it should have surface characteristics of a type that the coating materiels will adhorothoroto Thobsok supporting sheet can be whiteY in color or can beA infrared absorbent depending on the type of energy used to attain the development temperatures. lFor the backing sheet I have `found that various types of paper, such .as kraft paper serve very satisfactorily. Y Y i Y I apply a developer ooatos ombodyirig my invootiooto ono or, both of the Sorfaoos and. the bookies shoot., and.' es previously indicated, it may be at least partially absorbed therein. The developer coating includes an organic amine Whoh has low vapor pressure at 'ordinary .ambient tom- Poretufos; oooh es Jroom temperature or'tomporturos 1oW- er than 100 C., but which is sufficiently volatile and will volatilizo or tomporoturos between 109 and 180 Q.. Y .The amine selected should also be of a type which has noundesired otoot oo tho diazo and coupling oompoooss to tho sensitized layer of the reproduction sheet during the development Period Representative @minos 'Whoh mai bo used for this purpose are piperazine, t-,butyl-amine-ethanol, t-butyl diethanolamine, 'diethanolamine, aminoe'thylethanolamine, menthane diamine, aminoethyl-piperazine, 1.2,4-trimothylspiporazine, 2,6-t1imothYl-mofpholioio, ood

triothatlolamino- The orsanoamino ood may bo'oithor,

in Solid crystalline form, such as piporolfioo of t-butylamine-ethanol, or may be a liquid such as 2,6-,dimethylmorpholine. However, the organic `amine used should be one in which it is substantially non-volatile at ambient temperatures and which is. volatile at between 100^180 C. I `prefer to use .piperazine which gives very satisfactory results.

I prefer to include in the developer or coating` a reservoir of lwater which under normal .ambient temperatures is retained in combined `dry form but which is released when subjected to temperatures in excess of 100 C.. For this purpose I have found that crystalline salts having water of crystallization combined therewith ser-Ve Very satisfactorily. Examples of such salts are sodium acetate, sodium thiosulfate, sodium carbonate, sodium sulfate, magnesium sulfate, magnesium chloride and piperazine. Piperazine, when mixed with water becomes hydrated with the addition of six molecules of water to the piperazine molecule and when subjectedY to development temperature, the water is released; thus serves the double function of an amine and as a crystalline salt as a reservoir for water. The crystalline salts should preferably be selected and mixed together so as to provide a pH, close to'neutral. I have found that undesirable results Vare obtained if the coating ccntains strong non-volatile alkalies or acids. Thus, if the coating is highly alkaline,

the amine,k is prematurely released.k If the coating is excessively acid, the release or volatilization of the amine is delayed or retarded. I also prefer to include an acetate salt asl have found that this serves to neutralize any trace `of odor from the amine.

Under certain circumstances the crystalline salts may be omitted from the developer coat-ing andthe water supplied from other sources, such asy water absorbed in the backingv sheet.

The developer coating also may include suitable binders and adhesives, such as polyvinyl acetate, casein, or the like. Additionally, it preferably includes dispersing agents, such as finely milled silica, titanium oxide, clay, starch grains or absorptive materials like activated carbon or diatomaceous earth.

The developer coating may be applied to the backing sheet in aqueous solution or dispersion by conventional diazotype coating equipment. The proportions and quantities of materials applied to the backing sheet may be varied. I have found that satisfactory results are obtained if between 0.4 and 5.0 grams of organic amine and between 0.5 and 7.0 grams of crystalline salt having Acombined water of crystallization per squaremeter are applied to the backing sheet. Dispersing pigments in such concentrations as to yield coating weights of 0.5 to 5 grams per square meter .and binders or adhesives in the amount of from l0 to 100% in proportion to the organic amine have proved advantageous.

After the developer coating has been applied to the backing sheet, the coating may be suitably dried as in a high velocity air dryer at elevated temperatures but below I C.

Optionally, the opposite surface of the backing sheet may have applied thereto a coating containing some of the waterreservoir material or a coating identical to the one on the front side. This coating may comprise one or more of the indicated crystalline salts applied in aqueous solution by means of simple diazotype coating equipment. If an optional coating of this type is applied, satisfactory results are obtained if between 0.5 `and 6.0 grams per square meter are applied to the opposite surface of the backing sheet. After the second coating is applied, it may be simply dried as in a high velocity air dryer at a temperature below 100 C.

Developer sheet material thus prepared may be cut into individual sheets of a size to register with diazotype reproduction sheets with which it is to be used. If preferred, the developer sheet material may be supplied in roll form for use in a developing machine in which case the web of developer material is brought into contact with the exposed `diazotype reproduction sheet-s in the developing machine.

One of the advantages of my improved developer sheet is that it may be used for developing images on conventional diazo reproduction sheets of the two component type, such as used today in ammonia development systems. Typical diazo reproduction sheets of this type are formed of a backing sheet having a sensitized layer applied thereto, as shown in FIG. 2.

The sensitized layer includes a diazo compound, a coupling compound and an acidic stabilizing material. Representative diazo compounds used in such reproduction sheets are as follows: diazo of p-amino-diphenylamine, diazo of parnino-dimethylaniline, diazo of pamino-diethylaniline, diazo of p-amino-N-ethyl-N-hydroxy-ethyl-aniline, diazo of p-morpholino-aniline and diazo of 4morpholino2,5diethoxylaniline. Representative couplers used are as follows: resorcinol, 2,3-dihydroxynaphtalene. 2,3 dihydroxynaphtalene 6 sulfonic acid sodium salt, acetoacetanilide, 6,7-dihydroxy-2,3 disulfonic acid sodium salt. Representative acidic stabilizers are as follows: citric acid, tartaric acid, maleic acid, boric acid, sulfamic acid, and zinc chloride. Other nor-mal additions to sensitized layers may also be used, like thiourea, hydroxyethyl-allyl-thiourea, magnesium chloride and l,3,6-naphthalene-trisulfonic acid, sodium salt. For the purposes of my improved process, it is preferable that the diazo sensitized layer also includes a hygroscopic agent, such as glycerine, glycol -or a polyglycol as this favors and' accelerates the development process. It has been observed that when such agents are incorporated in the coating layer of the developer sheet, the rate of thermal development is adversely effected. However, when incorporated in the sensitized layer of the diazo reproduction sheet beneficial results are obtained.

In carrying out my improved process, the master which is to be reproduced is superimposed on the diazo reproduction sheet in the usual manner and is exposed to actinic radiation of the type to which the diazo material is sensitive (usually ultraviolet light or low wave length visible light) in the manner indicated in FIG. 2. The diazo materialin the exposed portions of the sensitized layer is decomposed by the actinic radiation while the diazo material protected by the opaque portions of the master remains unaiected. The exposed diazo reproduction sheet is then arranged in superimposed relationship with the developer sheet with t-he sensitive layer of the reproduction sheet in contact with the developer sheet. The superimposed sheets are then subjected to an elevated temperature within the indicated temperature range of between 100 and 180 C., preferably approximately 115 C., as in the manner indicated in FIG. 3. Thus, in FIG. 3 it will be seen that the superimposed sheets are rolled around a heated roller which is heated to a temperature of about 115 C. The speed at which the superimposed sheets are passed around the heated roll may vary so that the expose of the superimposed sheets to -heat from the heated roll may vary from 2% seconds to 30 seconds without any adverse eiect on the diazo reproduction or developer sheet. Upon heating of the developer coating, the organic amine volatilizes and the water of crystallization is released and the amine and moisture ultimately mix with the sensitized coating causing the undecomposed diazo material to combine with the coupling compound forming an azo dye in the unexposed portions of the reproduction sheet.

It should be understood that a reversal of the developer sheet and the sensitized diazo reproduction sheet will not alter the result as shown in FIG. 3. Moreover, the superimposed sheets may pass over the top of the heated roll and discharge at the bottom thereof.

The following are examples of developer sheet and the preparation thereof in accordance with my invention:

Example 1 On a conventional diazotype coating machine, a black kraft paper of pound basis weight is coated on a kiss roller airknife coating station, at a coating speed of 2,000 yards per hour with the following preparation:

The coated sheet is dried in a high velocity air dryer at a temperature of 70 C. and then the backside of the sheet is coated in the same machine in one and the same pass and on an identical coating station with the following solution of Water cc 650 Sodium thiosulfate (anhydrous) g 350 The sheet is finally dried under the same conditions as after the first coating. The sheet thus prepared is ready for use as developer sheet. The developer sheet thus prepared may be cut into individual sheets corresponding in size to the diazo reproduction sheets with which they are to be used or may be supplied in roll form.

In using the developer sheets a diazo reproduction sheet of the two component type suitable for ammonia development as indicated in column 4 `and commercially available such as Solar 410 F or Ozalid 200 SS, is exposed to actinic radiation with the master superimposed thereon. The exposed reproduction sheet is then arranged in superimposed relationship with the developer sheet with the sensitized coating in contact with the developer coating. Both sheets While in superimposed relationship are passed around a heated metal roller having a temperautre in excess of 115 C. for a period of Example 2 On a conventional diazotype coating machine, a white suliite, rosin sized, paper of 20 pound basis weight is coated on a kiss roller airknife coating station, at a coating speed of 2,400 yards per hour with the following preparation:

Water cc V650 Sodium acetate (anhydrous) g 130 Sodium .thiosulfate (andhydrous) g 45 Piperazinev (andhydrous) g 45 Non colloidal silica powder (Davison) g 45 Non-ionic polyvinyl-acetate dispersion g 65 The coated sheet is dried in a convection air dryer at a temperature of C. and then the backside of the sheet is coated on the same machine and on an identical coating station with the following solution of:

Water cc 900 Sodium sulfate (anhydrous) g The sheet is finally dried under the same conditions as after the first coating. The sheet thus prepared is ready for use as developer sheet.

In using the developer sheet for thermal development for diazotype reproductions the same procedure is followed as described in Example 1.

Example 3 On a conventional diazotype coating machine, a kraft paper of 40 pound basis weight is coated on a kiss roller airknife coating stati-on at a coating speed of 2,000 yards per hour with the following preparation:

Water cc 670 Sodium acetate (anhydrous) g 80 Sodium thiosulfate (anhydrous) g 50 t-Butyl-'amino-ethanol g 50 Non colloidal silica powder (Davison) g 50 Non-ionic polyvinyl-acetate dispersion g 100 The coated sheet is dried in a convection air dryer at a temperature of 70 C. and then the backside of the sheet is coated on the same machine and on an identical coating station with the following solution of Water cc 900 Sodium acetate (anhydrous) g 100 The sheet is finally dried under the same conditions as after the rst coating. The sheet thus prepared is ready for use as developer sheet.

In using the developer sheet for thermal development for diazotype reproductions the same procedure is followed as described in Example 1.

In the examples given above any of the other indicated organic amines and any of the other crystalline salts may -be substituted for those listed in the examples. Also, it will be appreciated that the proportions may be varied within the indicated limits.

It will thus be seen that I have provided an improved thermal diazotype printing process and lan improved developer sheet for use therein in which the shelf life of the print sheet is not alected; in which the development takes place at moderate temperatures within a reasonable period of time without damage to the dyes or backing sheet; and which produces prints of very satisfactory dye contrast, intensity and density.

' Modifications may be made in the illustrated drawing and examples without departing from the spirit and scope of my invention as defined in the appended claims.

I claim:

1. A thermal diazotype developer sheet comprising a backing sheet having applied thereto coating material which includes piperazine and a crystalline salt contain'- ing water of crystallization, said Water of crystallization being released when subjected to temperatures in the same temperature range at which the piperazine volatilizes.

2. The method of making a thermal diazotype print which comprises first providing a sensitized sheet having a backing sheet and a sensitized coating including a diazo compound, a coupling compound, an acidic stabilizing agent, and a hygroscopic agent, then superimposing a master to be reproduced over the sensitized sheet and subjecting the superimposed sheet to actinic radiation to cause the decomposition of the diazo compound in 4the exposed portions of the sensitized sheet, thereafter superimposing over the sensitized sheet a developer sheet having applied thereto coating material which includes piperazine `and a crystalline salt containing water of crystallization, said water of crystallization being released when subjected to temperatures in excess of 100 C., and subjecting said superimposed exposed sensitized sheet and 8 developer sheet to an elevated temperature between 100 C. and 180 C. to volatilize the piperazine and release the water of crystallization to thereby cause the coupling cornpound to combine with the diazo compound to form a dye in the unexposed portions of the sensitized sheet.

References Cited by the Examiner UNITED STATES PATENTS Y 2,308,058 1/43 Crowley 96-49 2,461,467 2/ 49 Easton. 2,653,126 9/53 Grieg 204-2 2,691,587 10/54 Grieg 96-49 2,774,669 12/ 56 Marron et al 96-49 2,949,409 8/ 60 Richards 204-2 3,046,128 7/ 62 Klimkowski et al. 96-49 3,076,707 2/ 63 Lawton et al 96-49 X 3,080,230 3/ 63 Haydn et al. 96-95 FOREIGN PATENTS 816,601 7/ 59 Great Britain. 1,249,913 11/60 France.

OTHER REFERENCES Kosar: Photographic Science and Engineering, vol. 5, No. 4, July-August 1961, pages 239-243.

NORMAN G. TORCHIN, Primary Examiner. 

2. THE METHOD OF MAKING A THERMAL DIAZOTYPE PRINT WHICH COMPRISES FIRST PROVIDING A SENSITIZED SHEET HAVING A BACKING SHEET AND A SENSITIZED COATING INCLUDING A DIAZO COMPOUND, A COUPLING COMPOUND, AN ACIDIC STABILIZING AGENT, AND A HYGROSCOPIC AGENT, THEN SUPERIMPOSING A MASTER TO BE REPRODUCED OVER THE SENSITIZED SHEET AND SUBJECTING THE SUPERIMPOSED SHEET TO ACTINIC RADIATION TO CAUSE THE DECOMPOSITION OF THE DIAZO COMPOUND IN THE EXPOSED PORTIONS OF THE SENSITIZED SHEET, THEREAFTER SUPERIMPOSING OVER THE SENSITIZED SHEET A DEVELOPER SHEET HAVING APPLIED THERETO COATING MATERIAL WHICH INCLUDES PIPERAZINE AND A CRYSTALLINE SALT CONTAINING WATER OF CRYSTALLIZATION, SAID WATER OF CRYSTALLIZATION BEING RELEASED WHEN SUBJECTED TO TEMPERATURES IN EXCESS OF 100*C., AND SUBJECTING SAID SUPERIMPOSED EXPOSED SENSITIZED SHEET AND DEVELOPER SHEET TO AN ELEVATED TEMPERATURE BETWEEN 100* C. AND 180*C. TO VOLATILIZE THE PIPERAZINE AND RELEASE THE WATER OF CRYSTALLIZATION TO THEREBY CAUSE THE COUPLING COMPOUND TO COMBINE WITH THE DIAZO COMPOUND TO FORM A DYE IN THE UNEXPOSED PORTIONS OF THE SENSITIZED SHEET. 